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<a name="regex"><strong>21. Regular Expressions</strong></a></font>
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<a name="overview"><strong>21.1 Overview</strong></a>
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<blockquote>
<p>
JMeter includes the pattern matching software <a href="http://attic.apache.org/projects/jakarta-oro.html">Apache Jakarta ORO</a>
<br>

There is some documentation for this on the Jakarta web-site, for example
<a href="http://archimedes.fas.harvard.edu/scrapbook/jakarta-oro-2.0.6/docs/api/org/apache/oro/text/regex/package-summary.html">
a summary of the pattern matching characters</a>
</p><p>
There is also documentation on an older incarnation of the product at
<a href="http://www.savarese.org/oro/docs/OROMatcher/index.html">OROMatcher User's guide</a>, which might prove useful.
</p><p>
<table border="1" bgcolor="#bbbb00" width="50%" cellspacing="0" cellpadding="2">
<tr><td>With JMeter version 5.5 the Regex implementation can be switched from Oro to the JDK based one by setting
the JMeter property <tt class="code">jmeter.regex.engine</tt> to some value different than <tt class="code">oro</tt>.</td></tr>
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</p>
<p>
The pattern matching is very similar to the pattern matching in Perl.
A full installation of Perl will include plenty of documentation on regular expressions - look for <tt class="code">perlrequick</tt>,
<tt class="code">perlretut</tt>, <tt class="code">perlre</tt> and <tt class="code">perlreref</tt>.
</p><p>
It is worth stressing the difference between &quot;<em>contains</em>&quot; and &quot;<em>matches</em>&quot;, as used on the Response Assertion test element:
</p><dl>
<dt>&quot;<em>contains</em>&quot;</dt><dd> means that the regular expression matched at least some part of the target,
so '<tt class="code">alphabet</tt>' &quot;<em>contains</em>&quot; '<tt class="code">ph.b.</tt>' because the regular expression matches the substring '<tt class="code">phabe</tt>'.
</dd>
<dt>
&quot;<em>matches</em>&quot;</dt><dd> means that the regular expression matched the whole target.
So '<tt class="code">alphabet</tt>' is &quot;<em>matched</em>&quot; by '<tt class="code">al.*t</tt>'.
</dd>
</dl><p>In this case, it is equivalent to wrapping the regular expression in <tt class="code">^</tt> and <tt class="code">$</tt>, viz '<tt class="code">^al.*t$</tt>'.
</p><p>However, this is not always the case.
For example, the regular expression '<tt class="code">alp|.lp.*</tt>' is &quot;<em>contained</em>&quot; in '<tt class="code">alphabet</tt>',
but does not &quot;<em>match</em>&quot; '<tt class="code">alphabet</tt>'.
</p><p>Why? Because when the pattern matcher finds the sequence '<tt class="code">alp</tt>' in '<tt class="code">alphabet</tt>', it stops trying any other
combinations - and '<tt class="code">alp</tt>' is not the same as '<tt class="code">alphabet</tt>', as it does not include '<tt class="code">habet</tt>'.
</p><p>
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Unlike Perl, there is no need to (i.e. do not) enclose the regular expression in <tt class="code">//</tt>.
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</p>
<p>
So how does one use the modifiers <tt class="code">ismx</tt> etc. if there is no trailing <tt class="code">/</tt>?
The solution is to use <i>extended regular expressions</i>, i.e. <tt class="code">/abc/i</tt> becomes <tt class="code">(?i)abc</tt>.
See also <a href="#placement">Placement of modifiers</a> below.
</p></blockquote>
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<a name="examples"><strong>21.2 Examples</strong></a>
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<blockquote>
<h3>Extract single string</h3><p>
Suppose you want to match the following portion of a web-page:
<br>

<tt class="code">name=&quot;file&quot; value=&quot;readme.txt&quot;&gt;</tt>
<br>

and you want to extract <tt class="code">readme.txt</tt>.
<br>

A suitable regular expression would be:
<br>

<tt class="code">name=&quot;file&quot; value=&quot;(.+?)&quot;&gt;</tt>
<p>
The special characters above are:
</p>
<dl>
<dt><tt class="code">(</tt> and <tt class="code">)</tt></dt><dd>these enclose the portion of the match string to be returned</dd>
<dt><tt class="code">.</tt></dt><dd>match any character</dd>
<dt><tt class="code">+</tt></dt><dd>one or more times</dd>
<dt><tt class="code">?</tt></dt><dd>don't be greedy, i.e. stop when first match succeeds</dd>
</dl>
<p>
Note: without the <tt class="code">?</tt>, the <tt class="code">.+</tt> would continue past the first <tt class="code">&quot;&gt;</tt>
until it found the last possible <tt class="code">&quot;&gt;</tt> - which is probably not what was intended.
</p>
<p>
Note: although the above expression works, it's more efficient to use the following expression:
<br>

<tt class="code">name=&quot;file&quot; value=&quot;([^&quot;]+)&quot;&gt;</tt>
where<br>

<tt class="code">[^&quot;]</tt> - means match anything except <tt class="code">&quot;</tt><br>

In this case, the matching engine can stop looking as soon as it sees the first <tt class="code">&quot;</tt>,
whereas in the previous case the engine has to check that it has found <tt class="code">&quot;&gt;</tt> rather than say <tt class="code">&quot; &gt;</tt>.
</p>
<h3>Extract multiple strings</h3>
<p>
Suppose you want to match the following portion of a web-page:<br>

<tt class="code">name=&quot;file.name&quot; value=&quot;readme.txt&quot;</tt>
and you want to extract both <tt class="code">file.name</tt> and <tt class="code">readme.txt</tt>.
<br>

A suitable regular expression would be:
<br>

<tt class="code">name=&quot;([^&quot;]+)&quot; value=&quot;([^&quot;]+)&quot;</tt>
<br>

This would create 2 groups, which could be used in the JMeter Regular Expression Extractor template as <tt class="code">$1$</tt> and <tt class="code">$2$</tt>.
</p>
<p>
The JMeter Regex Extractor saves the values of the groups in additional variables.
</p>
<p>
For example, assume:
</p>
<ul>
<li>Reference Name: <tt class="code">MYREF</tt></li>
<li>Regex: <tt class="code">name=&quot;(.+?)&quot; value=&quot;(.+?)&quot;</tt></li>
<li>Template: <tt class="code">$1$$2$</tt></li>
</ul>
<p>
<table border="1" bgcolor="#bbbb00" width="50%" cellspacing="0" cellpadding="2">
<tr><td>Do not enclose the regular expression in <tt class="code">/ /</tt></td></tr>
</table>
</p>

<p>
The following variables would be set:
</p>
<dl>
<dt><tt class="code">MYREF</tt></dt><dd><tt class="code">file.namereadme.txt</tt></dd>
<dt><tt class="code">MYREF_g0</tt></dt><dd><tt class="code">name=&quot;file.name&quot; value=&quot;readme.txt&quot;</tt></dd>
<dt><tt class="code">MYREF_g1</tt></dt><dd><tt class="code">file.name</tt></dd>
<dt><tt class="code">MYREF_g2</tt></dt><dd><tt class="code">readme.txt</tt></dd>
</dl>
These variables can be referred to later on in the JMeter test plan, as <tt class="code">${MYREF}</tt>, <tt class="code">${MYREF_g1}</tt> etc.
</p></blockquote>
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<a name="line_mode"><strong>21.3 Line mode</strong></a>
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<blockquote>
<p>The pattern matching behaves in various slightly different ways,
depending on the setting of the multi-line and single-line modifiers.
Note that the single-line and multi-line operators have nothing to do with each other;
they can be specified independently.
</p><h3>Single-line mode</h3><p>
Single-line mode only affects how the '<tt class="code">.</tt>' meta-character is interpreted.
</p><p>
Default behaviour is that '<tt class="code">.</tt>' matches any character except newline.
In single-line mode, '<tt class="code">.</tt>' also matches newline.
</p><h3>Multi-line mode</h3><p>
Multi-line mode only affects how the meta-characters '<tt class="code">^</tt>' and '<tt class="code">$</tt>' are interpreted.
</p><p>
Default behaviour is that '<tt class="code">^</tt>' and '<tt class="code">$</tt>' only match at the very beginning and end of the string.
When Multi-line mode is used, the '<tt class="code">^</tt>' metacharacter matches at the beginning of every line,
and the '<tt class="code">$</tt>' metacharacter matches at the end of every line.</p></blockquote>
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<a name="meta_chars"><strong>21.4 Meta characters</strong></a>
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<blockquote>
<p>
Regular expressions use certain characters as meta characters - these characters have a special meaning to the RE engine.
Such characters must be escaped by preceding them with <tt class="code">\</tt> (backslash) in order to treat them as ordinary characters.
Here is a list of the meta characters and their meaning (please check the ORO documentation if in doubt).
</p><dl>
<dt><tt class="code">(</tt> and <tt class="code">)</tt></dt><dd>grouping</dd>
<dt><tt class="code">[</tt> and <tt class="code">]</tt></dt><dd>character classes</dd>
<dt><tt class="code">{</tt> and <tt class="code">}</tt></dt><dd>repetition</dd>
<dt><tt class="code">*</tt>, <tt class="code">+</tt> and <tt class="code">?</tt></dt><dd>repetition</dd>
<dt><tt class="code">.</tt></dt><dd>wild-card character</dd>
<dt><tt class="code">\</tt></dt><dd>escape character</dd>
<dt><tt class="code">|</tt></dt><dd>alternatives</dd>
<dt><tt class="code">^</tt> and <tt class="code">$</tt></dt><dd>start and end of string or line</dd>
</dl><p>
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Please note that ORO does not support the <tt class="code">\Q</tt> and <tt class="code">\E</tt> meta-characters.
[In other RE engines, these can be used to quote a portion of an RE so that the meta-characters stand for themselves.]
You can use function  to do the equivalent, see <a href="functions.html#__escapeOroRegexpChars">${__escapeOroRegexpChars(valueToEscape)}</a>.
</td></tr>
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</p>
<p>
The following Perl5 extended regular expressions are supported by ORO.

<dl>
<dt><tt class="code">(?#text)</tt></dt>
<dd>An embedded comment causing text to be ignored.</dd>
<dt><tt class="code">(?:regexp)</tt></dt>
<dd>Groups things like &quot;<tt class="code">()</tt>&quot; but doesn't cause the group match to be saved.</dd>
<dt><tt class="code">(?=regexp)</tt></dt>
<dd>A zero-width positive lookahead assertion. For example, <tt class="code">\w+(?=\s)</tt> matches a word followed by whitespace, without including whitespace in the MatchResult.</dd>
<dt><tt class="code">(?!regexp)</tt></dt>
<dd>A zero-width negative lookahead assertion. For example <tt class="code">foo(?!bar)</tt> matches any occurrence of &quot;<tt class="code">foo</tt>&quot; that
isn't followed by &quot;<tt class="code">bar</tt>&quot;. Remember that this is a zero-width assertion, which means that <tt class="code">a(?!b)d</tt> will
match <tt class="code">ad</tt> because <tt class="code">a</tt> is followed by a character that is not <tt class="code">b</tt> (the <tt class="code">d</tt>) and a <tt class="code">d</tt>
follows the zero-width assertion.</dd>
<dt><tt class="code">(?imsx)</tt></dt>
<dd>One or more embedded pattern-match modifiers. <tt class="code">i</tt> enables case insensitivity, <tt class="code">m</tt> enables multiline treatment
of the input, <tt class="code">s</tt> enables single line treatment of the input, and <tt class="code">x</tt> enables extended whitespace comments.</dd>
</dl>
<b>Note that <tt class="code">(?&lt;=regexp)</tt> - lookbehind - is not supported.</b>
</p></blockquote>
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<a name="placement"><strong>21.5 Placement of modifiers</strong></a>
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<blockquote>
<p>
Modifiers can be placed anywhere in the regex, and apply from that point onwards.
[A bug in ORO means that they cannot be used at the very end of the regex.
However they would have no effect there anyway.]
</p><p>
The single-line <tt class="code">(?s)</tt> and multi-line <tt class="code">(?m)</tt> modifiers are normally placed at the start of the regex.
</p><p>
The ignore-case modifier <tt class="code">(?i)</tt> may be usefully applied to just part of a regex,
for example:</p><div align="left">
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<td bgcolor="#023264" width="1" height="1"><img src="/images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"/></td>
<td bgcolor="#023264" height="1"><img src="/images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"/></td>
<td bgcolor="#023264" width="1" height="1"><img src="/images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"/></td>
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<td bgcolor="#ffffff"><pre>
Match ExAct case or (?i)ArBiTrARY(?-i) case
</pre></td>
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<td bgcolor="#023264" height="1"><img src="/images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"/></td>
<td bgcolor="#023264" width="1" height="1"><img src="/images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"/></td>
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<tt class="code">Match ExAct case or arbitrary case</tt><tt class="code">Match ExAct case or ARBitrary case</tt><tt class="code">Match exact case or ArBiTrARY case</tt></blockquote>
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<a name="testing_expressions"><strong>21.6 Testing Regular Expressions</strong></a></font>
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<blockquote>
<p>
Since JMeter 2.4, the listener <a href="component_reference.html#View_Results_Tree">View Results Tree</a>
include a RegExp Tester to test regular expressions directly on sampler response data.
</p><p>
There is a <a href="http://www.regexplanet.com/advanced/java/index.html">Website</a> to test Java Regular expressions.
</p><p>
Another approach is to use a simple test plan to test the regular expressions.
The Java Request sampler can be used to generate a sample, or the HTTP Sampler can be used to load a file.
Add a Debug Sampler and a Tree View Listener and changes to the regular expression can be tested quickly,
without needing to access any external servers.
</p></blockquote>
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